Research subject. This article considers accessory minerals, which, unlike zircons, are present in the vast majority of common clastic rocks. Materials and methods. The data on the chemical composition of minerals (garnet, tourmaline, chromespinelide, rutile, chloritoid and clinopyroxene) extracted from the Riphean and Vendian, as well as Upper Permian and Lower Triassic sandstones of the Southern Urals, were used to illustrate the features of applying various methods and techniques. In addition, numerous examples from publications are presented. Results. A number of modern methods for studying accessory minerals, which might be used to elucidate the composition and characteristics of the provenance rocks for terrigenous strata, were reviewed. Conclusions. It is shown that, similar to zircons, accessory minerals possess a significant potential in terms of providing important data on parent rocks.

Research subject. The Late Paleozoic (D3–P1) black shale strata surrounding the Kara Astrobleme (Pay-Khoy) were studied. Materials and methods. The rocks were sampled radially along the profile from the edge of the astrobleme (the at the contact zone with impactites) with access to black shales that were not affected by post-impact transformations. An analysis of the mineralogical and geochemical features of the black shales surrounding the Kara astrobleme was carried out using a complex of modern research methods (Geonauka Centre for Collective Use, IG FRC Komi Scientific Centre, Ural Branch of the Russian Academy of Sciences) in order to identify the possible mobilisation, re-deposition and concentration of ore matter under the conditions of intensive post-impact hydrothermal altering. Results and conclusions. The geochemical features of the black shale deposits altered by post-impact hydrothermal processes in the vicinity of the Kara impact structure were determined. The sharp abnormal contents of Mn, B, Zr, Sr, Ge, Cd, Hf, Se and Eu as well as the abnormal contents of Ti, Ba, Cr, Rb, Li, Ce, La, Ga, Sc, Co, Cs, Gd, Dy and W were revealed. The geochemical concentration specificity of components in different regions of the Kara astrobleme associated with the specialisation of target rocks was established. Raremetal and rare-earth minerals, sulphides and thymannite (HgSe) were diagnosed.

Research subject. This research was focused on the most common mineralized tissue that composes conodont elements. The aim was to investigate the characteristics of the composition and structure of this tissue and to reconstruct its formation process. Materials and methods. The work was based on a collection of well-preserved conodont elements from the Upper Devonian of the East European Platform and the Upper Devonian – Lower Carboniferous of the east of the Pechora Plate. Oriented and polished thin sections made from some of the elements were studied using light and electron microscopy, as well as a microhardness tester. Energy dispersive spectroscopy was used to determine the chemical (elemental) composition of the lamellar tissue. In addition, the carbon isotope ratio was determined for organic matter. Results. The study showed that the lamellar tissue in conodont elements consists of fluorohydroxylapatite crystallites of various morphology, surrounded by organic matter, which makes up 2–3% of the tissue. Variations in the composition of major elements incorporated in fluorohydroxylapatite of the lamellar tissue are insignificant. Organic matter is represented by a collagen-like protein, likely to be of a non-fibrillar type, with a light carbon isotopic composition (–26.2 ‰ PDB). The lamellar tissue has an average microhardness of 2.6 GPa, the variations of which are due to textural and structural features and the distribution of organic matter. In conodont elements, the lamellar tissue is in contact with other types of tissue. Transitions between tissues are relatively sharp at the borders of the lamellae and gradual within the same lamella. Conclusions. A model was developed, according to which the growth cycle of a conodont element covered the sequential formation of two lamellae preceded by the resorption of one external lamella. In the structures formed by the lamellar tissue, both lamellae consisted of this tissue. The lamellar tissue is of interest as a natural model of an organic-mineral composite based on protein and calcium phosphate.

Research subject. The isotopic composition (Pb-Pb, Sm-Nd, Rb-Sr, Os/Os, Hf/Hf, ³ He/⁴ He, etc.) of magmatic complexes and ore-magmatic systems (OMS) of two ore clusters (Kupolsky and Ilirneysky) located in the subpolar Western Chukotka was studied. These ore clusters differ from each other both in their structural position and the age of their magmatic complexes, within which the largest deposits of Au-Ag type are known. Materials and methods. The Pb-Pb, Rb-Sr, SmNd, Re-Os, Lu-Hf, ³ He/⁴ He, ⁴⁰Ar/³⁶Ar and sulphur isotopic systems were studied at the VSEGEI centre for isotopic studies (St. Petersburg), as well as at the Institute of Geology, Geochemistry and Ore Deposits (IGEM, Moscow) and the Laboratory of Stable Isotopes of the Far Eastern Geological Institute (FEGI, Vladivostok). Re and Os were measured using an ELEMENT-2 inductively coupled plasma single-collector mass spectrometer. Sulphur isotopic ratios were measured using a Finnigan MAT 253 isotope mass spectrometer. Results and conclusions. On the basis of the isotope-geochemical data obtained, an assumption was made that various deep sources participated in the magma generation, and the differentiated composition of late melts may reflect the melting processes of the crust upper horizons. When comparing the data on the magmatism of the Ilirneysky and Kupolsky ore clusters, a different degree of crustal rock influence on melt generation was revealed. The Kupolsky ore cluster is characterised by a large influence of mantle sources in intraplate magmatism associated with ore formation processes. This is likely to have determined a greater amount of mineralisation in the Kupolsky cluster compared to the Ilirneysky ore cluster.

Research subject. The geological structure and rock composition of the Nizhne-Sinyachikhinsky plagiogranite massif, which is part of the Alapaevsk-Sukholozhsky zone, is promising for the Cu(Au,Mo)-porphyric mineralization type, were studied. The aim was to determine the formation features of these rocks and compare them with the productive granitoids of Ural porphyry deposits of similar age. Materials and methods. The mineral composition of the rocks was determined using a JEOL JSM 6790LV scanning electron microscope with an INCA Energy 450 X-Max 80 EDS spectrometer and a CAMECA SX-100 electron microprobe analyser. The rock composition was obtained by X-ray fluorescence spectrometry on a SRM-35 and XRF-1800 spectrometers with the titrimetric determination of FeO. The concentrations of rare and rare-earth elements were determined on an ELAN 9000 inductively coupled plasma mass spectrometer at the Geoanalitik Center for Collective Use of the Ural Branch of the Russian Academy of Sciences. Results. For the first time, an early tonalite-plagiogranite series was identified in the structure of the massif. This series is represented by tonalites of the hypabyssal appearance, broken through by the dikes of plagiogranite-porphyry. It was shown that the separation of plagiogranite-porphyry melts from magmas of the mafic composition occurred at the base of the island-arc construction, and their crystallisation was carried out in an intermediate chamber at a pressure of 1.8–2.3 kbar. In contrast, the plagiogranites of the main phase of the massif were separated from the parent melt in an intermediate chamber located at the level of the upper crust, and their crystallisation occurred at a pressure of 1.5–2.0 kbar. Conclusions. A comparison of the main phase plagiogranites and the isolated early-series plagiogranite-porphyry indicates their similar composition, as well as their similarity in age with the granitoids of the Southern Urals, productive in terms of the porphyry mineralisation type. The concentrations of F, Cl and S in the apatites and amphiboles of the rocks under study is an argument in favour of their belonging to andesitoid formations that are productive in terms of the Cu (Au)-porphyry mineralisation type. The absence of the sulphide mineralisation of this type can be explained by a more significant depth of rock formation and their erosion section.

Research subject. The article presents the results of dating two dolerite dikes differing in geochemical features from a section along the Iset river in the area of Smolinskoe settlement (the Eastern zone of the Middle Urals). Materials and methods. The dating was performed by an U-Pb ID-TIMS technique for single zircon grains using an artificial ²⁰⁵Pb/²³⁵U tracer in the laboratory of geochronology and isotope geochemistry of the Geological Institute of the Kola Science Centre of the Russian Academy of Sciences. The lead isotopic composition and uranium and lead concentrations were measured using a Finnigan-MAT (RPQ) seven-channel mass spectrometer in dynamic mode using a secondary electron multiplier and RPQ quadrupole in ion counting mode. Results. The dikes were dated 330 ± 3 Ma and 240 ± 2 Ma. Conclusions. The research results indicate different ages of dolerite dikes developed within the Eastern zone of the Middle Urals. The oldest of the two established age levels corresponds to the Early Carboniferous era. This fact, along with the proximity of the dolerites to the petrochemical features of the basaltoids of the Early Carboniferous Beklenischevsky volcanic complex, allows these bodies to be considered as hypabyssal comagmates of these volcanics. The youngest obtained age level – Triassic – indicates that the introduction of some dolerite dikes was associated with the final phases of the trapp formation developed rarely within the eastern outskirts of the Urals and widely further east in the foundation (pre-Jurassic basement) of the West-Siberian Plate.

Research subject. The Koytash ore field is located in the potentially productive Au, Ag, W, Mo, Ti, Fe, Cu, Pb, Zn and REE North Nuratau mineralisation zone of Tien Shan. The authors undertook a study of the composition of dikes breaking through the Paleozoic ore-bearing formations, as well as their petro- and ore-generating role in the formation of the Koytash-Ugat sulphide-rare-metal (W, Mo, Fe) specialised mineralisation. Materials and methods. A study of rock and mineral composition was performed at the Institute of Geology and Geophysics named after Kh.M. Abdullaev. The content of petrogenic and rare elements in rocks and sulphides was determined by ICP-MS using an ICPE-9000 mass-spec trometer in the Central Laboratory of the State Committee for Geology of the Republic of Uzbekistan. The chemical analysis of minerals was performed using a Jeol-8800Rh electronic microanalyser at the Institute of Geology and Geophysics named after Kh.M. Abdullaev. The micrographs of transparent sections were obtained using Nikon Optiphot 2 Pol and Polam R-311 microscopes. Results and conclusions. The conducted study showed that, in terms of their structure, the Koytash ore field dike formations can be regarded as lamprophyres. In terms of their chemical composition, these formations are mafic and intermediate rocks of the subalkaline series. It was found that the composition of lamprophyre dikes correlates with the size of the erosion section. Their melanocratic varieties are confined to the southern part of the intrusion (absolute elevations are 1000–1200 m), and leucocratic – to the northern (about 1900 m). This is assumed to be the result of crystallization differentiation of a single initial melt. The dikes of the Koytash ore field lamprophyres break through not only sulphide-rare-metal bodies of the Koytash-Ugat strip, but also skarn and carbonate rocks and, in turn, are broken through by quartz-polymetallic ore-bearing veins, which testifies to their inter-ore character.

Research subject. The Mississippi Valley type deposits make up about a third of the global balance of lead and zinc reserves, resources and production. Additionally, silver, antimony, arsenic, barium, bismuth, cadmium, cobalt, gallium, indium, mercury, molybdenum, nickel and thallium can be present in the ores of these deposits. In the North-East of Russia, the Mississippi Valley type of deposits is poorly represented. In this work, we investigate the deposits of the Sardana ore cluster of the Republic of Sakha (Yakutia) and individual deposits of the Magadan region. Materials and methods. The article discusses the results of previous scientific research and new data on the geochemical features, isotopic composition of ores and geological and structural conditions for the formation of the Sardana cluster deposit. In addition, the potential for identifying stratiform lead-zinc deposits is associated with favourable geodynamic conditions in the region, as well as with the refinement and adaptation of the forecast-search model of MVT deposits for the North-East of Russia. Results. The mineralogical and geochemical features of the rocks and ores of the Sardana cluster deposits, the morphology of ore bodies, their zoning elements, as well as isotopic ratios indicate that the ores are likely to be of the Mississippi Valley type with the onset of ore deposition at early diagenetic and catagenetic stages. The distribution of rare elements indicates a significant role of superimposed metamorphism of the host carbonate-terrigenous strata in the deposition of the ores of producing stages. Conclusion. The potential possibility of increasing the mineral and raw material base of lead and zinc is associated with the identification of sedimentary basins with a stagnant anoxic regime of carbonate accumulation in the immediate vicinity of the development areas of rift complexes, as well as with the presence of other critically important forecast-search signs. In addition to the well-known Killakh metallogenic zone, Tuora-Sis and Orulgan metallogenic taxa located in the north of the Republic of Sakha (Yakutia) with known stratiform manifestations of lead and zinc belong to such areas.

Research subject. The article presents the results of a study of sedimentation rate and physical properties of bottom sediments in the Angara reservoirs under controlled level regimes. Materials and methods. The work was based on the materials of fieldwork carried out by the author on the Angara reservoirs in 1972–2017 and open-access literature sources. The physical properties and particle size distribution of bottom sediments were determined by the standard methods of engineering geology. Results. It was found that the controlled level regime determines the time cycles of sedimentation in reservoirs, sources of sediment-forming material, sedimentation rate and ambiguity of the physical properties of bottom sediments. Conclusions. During transgressions, sands, coarse aleurites and fine-aleurite silts accumulate in reservoirs most intensively; however, during regressions, coarse aleurites and aleurite-clayey silts are accumulated. During transgressions, all types of sediments are characterised by the highest sediment density, sediment skeleton density and absorption capacity, while coarse aleurites and fine-aleurite silts exhibit high natural humidity levels. In addition, coarse aleurites are characterised by a high porosity, while fine-aleurite and aleurite-clayey silts are characterised by a high content of organic matter. During regressions, the porosity of sands, fine-aleurite and aleurite-clayey silts increases, the content of organic matter in sands and coarse aleurites increases, and all types of sediments become more saturated with carbonates.

Subject. The aim of the work is to study the mechanism and sources of water formation, as well as the peculiarities of carbonate mineralization in the aquifer of the Kyndyg thermal water deposit. Materials and methods. The samples of water (8) and deposited carbonates (15), collected at different seasons at three sites, characterized by different temperatures and distances from the source, were investigated. pH, Eh, and electrical conductivity were determined by an electrochemical method. For the determination of HCO³ – , Cl– , SO₄ ²–, titrimetric, mercurymetric and turbidimetric methods were used. Trace element composition was determined by ICP-MS (NexION 300S); strontium isotopic composition – by MC-ICP-MS (Neptune Plus) using the bracketing technique after Sr chromatographic separation. Results. The chloride-calcium hydrochemical type prevails in the studied waters. A number of trace elements in water exceeds the clarke concentrations for groundwater in the supergene zone of mountain landscapes. ⁸⁷Sr/⁸⁶Sr isotope ratios (0.7065–0.7072) in thermal waters suggest that their composition is determined rather by the isotopic characteristics of the rocks through which water drains than by the influence of sea water. Among the newly formed carbonates, aragonite prevails. In contrast to thermal water, the concentrations of most metals in carbonates are below the clarke values; only Sr and Se are increased, which content is significantly increased in water as well. Deposited carbonates are characterized by ⁸⁷Sr/⁸⁶Sr values (0.7028–0.7074), which are lower than in the source thermal waters. Conclusions. On the basis of hydrogeological, hydrochemical and geochemical data, it can be assumed that the waters of this aquifer complex are formed mainly due to fresh fractured karst waters of lower Cretaceous limestones with submerged monocline dipping into the zone of slow circulation and mixing with sedimentogenic sodium chloride waters. The geochemical data and the presence of scandium anomaly suggest that the underlying Jurassic volcanogenic rocks also participate in water exchange.